Zebra Mussel

Dreissena polymorpha

Young zebra mussels often settle on top of older, bigger mussels, creating large colonies. (Dan Minchin/Public Library of Science)

The zebra mussel is a tiny bivalve with zebra-like stripes on its triangular shell. It lives in freshwater lakes, rivers, streams and reservoirs in parts of the Chesapeake Bay watershed. It is a non-native and invasive species.

Appearance:

The zebra mussel usually grows to less than one inch in length. Its D-shaped or triangular shell is patterned with dark (usually brown) and light stripes. The shell's flattened bottom allows the zebra mussel to stand up straight on a flat surface.

Habitat:

Lives in still or slow-moving freshwater lakes, rivers, streams and reservoirs. Uses its thin, strong threads to attach to solid, underwater surfaces, including rocks, pilings, pipes, buoys, boat hulls and native freshwater mussels and clams, limiting their ability to move and often smothering them.

Range:

Found in the Upper Bay and in parts of the Susquehanna River and its tributaries in New York, Pennsylvania and Maryland. Native to the Black, Caspian and Azov seas in Eurasia.

Feeding:

This stationary filter feeder draws in water through a siphon in order to filter out plankton and other food particles. Unused particles are ejected through a second siphon.

Predators:

Reproduction and Life Cycle:

Spawning occurs once water temperatures warm in spring and summer. Females can release more than one million eggs into the water in a single spawning season. Free-swimming larvae drift in the water for a few months, during which time currents transport them throughout river systems. Larvae anchor themselves to hard surfaces with thin, strong threads secreted from a gland on the foot. Young often settle on top of older, bigger mussels, forming large colonies. Zebra mussels typically live three to nine years, although some can live as long as 15 years.

Other Facts:

This invasive species was introduced to the Great Lakes region in the mid-to-late 1980s, likely via ballast water from a European ship. From there, zebra mussels spread rapidly throughout the United States